Combined tire pressure monitoring and keyless entry receiver

ABSTRACT

A system for monitoring conditions within a tire ( 12 ) including a sensor assembly ( 14 ) including a pressure sensor ( 36 ), an accelerometer ( 34 ), a temperature sensor ( 32 ), and a transmitter ( 40 ) to transmit signals indicative of current tire conditions. A remote transmitter ( 22 ) for actuating a remote keyless entry system ( 19 ) emits a signal to actuate a function of the keyless entry system ( 19 ) such as unlocking doors ( 20 ) of the motor vehicle ( 10 ). A receiver assembly ( 16 ) includes an amplitude shift keyed receiver ( 52 ) and a frequency shift keyed receiver ( 58 ) selectively engagable to receive radio frequency transmissions from the tire monitoring system or the remote keyless entry system ( 19 ).

REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of pending U.S. patentapplication Ser. No. 10/079,665 filed Feb. 20, 2002 now U.S. Pat.No.6,885,282 that claims priority to U.S. Provisional Patent ApplicationSer. No. 60/276,210 filed Mar. 15, 2001; 60/269,959 filed Feb. 20, 2001;60/276,325 filed Mar. 16, 2001; 60/298,258 filed Jun. 14, 2001;60/290,923 filed May 15, 2001; and 60/352,489 filed on Jan. 23, 2002.

BACKGROUND OF THE INVENTION

This invention relates to a system for monitoring conditions within atire, and specifically to a receiver assembly for receivingtransmissions of varying modulations from sensor assemblies within eachof the tires and from a remote keyless entry system. It is becomingincreasingly desirable to continually monitor tire pressures in a motorvehicle during operation. Such constant monitoring of tire pressuresallows an operator to maintain vehicle tire pressures within an optimalrange to optimize fuel economy and handling performance.

Conventional methods of monitoring tire pressure include positioning asensor within each wheel to monitor pressure. The sensor assemblytypically emits a radio frequency (RF) transmission indicative of tireconditions. A receiver disposed within the vehicle receives the RFsignal and actuates a messages or warning light to signal the operatorof tire conditions.

Many motor vehicles include a remote keyless entry system including akey fob carried by an operator to actuate door locks or other features.The remote keyless entry system includes a receiver disposed within themotor vehicle to receive transmissions from the key fob and actuatevehicle systems in response to transmissions received from the key fob.Some systems utilize the same type of transmission for the tiremonitoring system and the remote keyless entry system.

Typically, a signal transmission is modulated either as an amplitudeshift keyed ASK, or a frequency shift keyed FSK radio frequency. The ASKtransmission modulation is best suited for applications in which thereceiver and transmitter are relative stationary to each other. Inaddition ASK transmissions are favorable when there exists a relativelylong distance between the transmitter and the receiver. However, an ASKtransmission becomes disrupted when the receiver or transmitter aremoving relative to one another. The FSK signal is suited fortransmitters that are moving relative to the receiver because theamplitude remains essentially constant for the duration of anytransmission. However, the FSK transmission has lower peak fieldstrength than a comparable ASK transmission. The FSK transmission isspecifically suited for use with the sensor assembly disposed within thetire and the ASK transmission is best suited for use with the remotekeyless entry system.

Accordingly, it is desirable to develop a receiver capable of receivingboth ASK and FSK transmissions to optimize the capabilities of both thetire monitoring system and the remote keyless entry system.

SUMMARY OF THE INVENTION

An embodiment of this invention is a receiver assembly comprised of anamplitude key shifted (ASK) receiver and a frequency shift keyed (FSK)receiver for receiving transmissions from sensor assemblies mountedwithin each of the tires, and from a remote keyless entry system.

A system for monitoring conditions within tires mounted to a motorvehicle includes five tires, each with a sensor assembly. Each of thesensor assemblies gathers data indicative of conditions within the tireand transmits that data to a receiver assembly. The receiver assembly inturn forwards that data to a vehicle controller. The vehicle controllerwill then process the data for display to the operator of the motorvehicle.

Each tire mounts to a rim and each sensor assembly is mounted within therim and includes a valve stem and a circuit housing. The sensor assemblyincludes a sensor circuit disposed within the circuit housing. Thesensor circuit includes a temperature sensor, a motion sensor and apressure sensor. An RF transmitter receives data gathered by thesensors, and relays that data to the receiver.

Each transmission from the various sensor assemblies includes a uniqueidentity code relating to a specific sensor assembly. An initializationor learning mode defines specific sensor assemblies disposed on aspecific motor vehicle. Learning the specific identity codes of thesensor assemblies eliminates errant reception of other transmissionsfrom other sensor assemblies installed on other motor vehicles withinclose proximity.

The data transmitted from each of the sensor assemblies to the receiveris transmitted at predetermined intervals. There is a probability thatthe receiver will receive two or more data transmissions from differentsensor assemblies at the same time. The receipt of two or more datatransmission simultaneously or overlapped is known as a data collision.The receiver will not recognize collided data or overlapping datatransmission, therefore the current invention prevents overlapping datatransmissions by varying the interval between data transmission in arandom manner. Another factor considered in preventing signal collisionis the transmission rate that affects the length of time required totransmit data indicative of tire conditions. The faster data istransmitted and received the lower the probability of data collision.The shorter the total transmission time, the lower the probability ofsignal collision.

The receiver assembly comprises an amplitude shift key (ASK) receiverand a frequency shift keyed (FSK) receiver. The FSK receiver receivessignals from the sensor assemblies. The ASK receiver receives signalsfrom a key fob for a remote keyless entry system to initiate the lockingor unlocking of doors.

The ASK transmissions are favorable for situations where the transmitterand receiver are substantially stationary. The ASK radio frequencytransmission is easily disrupted by abrupt changes in received fieldstrength and therefore are not favorable for sending transmissions froma moving object such as the tires of a motor vehicle. However, the ASKprovides for greater signal power which is desirable for the remotekeyless entry system. The FSK transmissions are favorable for conditionswere the transmitter or receiver is moving during data transmission.However, an FSK transmission is amplified upon receipt, effectivelyremoving any amplitude disturbances.

The receiver assembly switches between the ASK receiver and the FSKreceiver in response to a triggering event. The triggering event is thevehicle speed. At speeds indicative of traveling along a roadway, theFSK receiver is engaged. As appreciated, a motor vehicle traveling atspeed along the roadway does not require reception of ASK transmissionsfrom a remote keyless entry transmitter to unlock the doors of the motorvehicle. Conversely, a vehicle at rest or parked is unlikely tospontaneously encounter a tire puncture, and therefore at lower speedsthe ASK receiver is engaged.

An intermediate condition is encountered when the motor vehicle isidling. In this condition, the receiver assembly engages the ASKreceiver due to the low speed of the vehicle, however, the tire maybecome punctured or encounter a condition that changes conditions withinthe tire. The signal from the sensor assemblies includes an ASK wake upsignal that proceeds the FSK signal transmitting data indicative ofcurrent conditions within the tire. The ASK wake up signal triggers thechange over from the ASK receiver to the FSK receiver. The FSK receiverremains engaged until the FSK transmission is completed and the ASKreceiver is reengaged.

The system of this invention includes a receiver capable of receivingboth ASK and FSK transmissions to optimize the capabilities of both thetire monitoring system and the remote keyless entry system.

BRIEF DESCRIPTION OF THE DRAWINGS

The various features and advantages of this invention will becomeapparent to those skilled in the art from the following detaileddescription of the currently preferred embodiment. The drawings thataccompany the detailed description can be briefly described as follows:

FIG. 1 is a schematic view of a motor vehicle including a tiremonitoring and remote keyless entry system;

FIG. 2 is a cross-sectional view of a tire including a sensor assembly;

FIG. 3 is a cross-sectional view of the sensor assembly mounted withinthe tire;

FIG. 4 is a side view of a sensor assembly;

FIG. 5 is a top view of the sensor assembly;

FIG. 6 is an exploded view of the sensor assembly;

FIG. 7 is a schematic view of the circuit assembly within the sensorassembly;

FIG. 8 is a schematic view of the components of a transmission from thesensor assembly;

FIG. 9 is a graphical representation of the format of data packetscomprising the transmission from the sensor assembly;

FIG. 10 is a graph illustrating the effect of transmission rate onsignal overlap in prior art systems;

FIG. 11 is a graph illustrating how increased transmission rate preventsdata overlap;

FIG. 12 is a schematic view of the receiver assembly;

FIG. 13 is a schematic view of a motor vehicle and an externaltriggering device to initialize the sensor assemblies;

FIG. 14 is a schematic view of a method of determining sensor assemblyposition; and

FIG. 15 is a schematic view of another embodiment of determining sensorassembly position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

An embodiment of this invention is a system for monitoring conditionswithin tires mounted to a motor vehicle 10 shown schematically inFIG. 1. The motor vehicle 10 includes four tires 12 along with anadditional tire 12 carried as a spare. Each of the tires 12 includes asensor assembly 14. Each of the sensor assemblies 14 gathers dataindicative of conditions within the tire 12 and transmits that data to areceiver assembly 16.

The receiver assembly 16 in turn forwards that data to a vehiclecontroller 18. The vehicle controller 18 will then process the data fordisplay to the operator of the motor vehicle 10 or to the remote keylessentry system 19 to actuate unlocking of doors 20 or other such functionsas are known to a worker skilled in the art. Preferably the remotekeyless entry system 19 is an active system requiring actuation, such asby depressing buttons on the key fob 22, however, it is within thecontemplation of this invention for passive remote keyless entry systemthat do not require a positive action by the operator.

Referring to FIGS. 2 and 3, each tire 12 mounts to a rim 24. Each sensorassembly 14 is mounted within the rim 24 and includes a valve stem 26and a circuit housing 28. The circuit housing 28 is preferably mountedwithin the tire 12 and the valve stem 26 extends from the circuithousing 28 outward to provide a means of filling the tire 12 with air. Asensor circuit 46 disposed within the circuit housing 28 preferablyincludes a pressure sensor 36, a temperature sensor 32 and anaccelerometer 34.

Referring to FIGS. 4–6, the valve stem 26 is pivotally mounted to thecircuit housing 28 to provide for use in rims 24 of variousconfigurations. The valve stem 26 is pivotally mounted to the circuithousing 28 and locked in a desired pivotal location by a lock nut 30.Pivotal adjustment of the valve stem 26 relative to the circuit housing28 allows for use of the sensor assembly 14 with various configurationsof wheel rims 24 (FIGS. 3 and 4).

FIG. 7, is a schematic view of the sensor circuit 46 disposed within thecircuit housing 28. The sensor circuit 46 includes the temperaturesensor 32, the accelerometer 34 and the pressure sensor 36. Each of thesensors 32, 34 and 36 are of any configuration known to a worker skilledin the art. An RF transmitter 40 receives data gathered by the sensors32, 34, and 36 and transmits that data to the receiver 16.

A battery 38 powers the sensor circuit 46. A battery monitor 40 measurebattery 38 power and provides a warning indicator that is sent to thereceiver assembly 16 when remaining battery power attains a desiredlevel. The receiver assembly 16 forwards the low battery signal to thevehicle controller 18 and in turn to the operator. Preferably the lifeof the battery 38 is of an extended length such that any necessarybattery change is infrequent throughout the life span of the motorvehicle 10. A controller 42 controls how the RF transmitter 42 emitsdata indicative of tire conditions.

The sensor circuit 46 also includes a low frequency receiver 42. The lowfrequency receiver 42 receives signals generated to initiate thetransmission of an identity code 68 (FIG. 8) from the sensor assembly 14in order to initialize and localize the sensor assembly 14.Initialization of the sensor assembly 14 teaches the receiver assembly16 the identity codes of each sensor assembly 14 installed on the motorvehicle 10 so that the receiver assembly 16 can ignore transmissionreceived from sensor assemblies 14 of other motor vehicles. Localizationteaches the receiver 16 and controller 18 the specific tire position ofthe sensor assembly 14 on the particular vehicle. The tire positionincludes left front tire, right front tire, left rear tire, and rightrear tire.

Referring to FIG. 8, a transmission 64 emitted by the sensor assembly 14includes an ASK wakeup signal 66, an identity code 68 and a data signal70. The transmission 64 is a FSK transmission, except for the ASK wakeup signal 66.

Referring to FIG. 9, each data transmission 64 includes a number of dataframes 72. Preferably, three (3) data frames 72 are sent for eachtransmission 64. The data transmitted from the sensor assemblies 14 tothe receiver assembly 16 are transmitted at predetermined intervals 80.There is a probability that transmissions from the various sensorassemblies 14 to the receiver assembly 16 will arrive at the same time(schematically indicated at 78). The receipt of two or more data frames72 simultaneously or overlapped, as shown at 78, is known as a datacollision. The receiver assembly 16 will not recognize collided oroverlapping data transmission because the overlapped data frames 78 areof a greater duration than the receiver assembly 16 is programmed toreceive. Overlapping data frames 72 cause the receiver assembly 16 toignore the data frames 78. Repeated data collisions would eliminate datatransmitted from at least two of the sensor assemblies 14.

The system of this invention includes a method of preventing repeateddata collisions. The sensor assemblies 14 of this invention preventoverlapping data frames 72 by varying the predetermined interval 80between data frames 72 in a random manner. The length of the data frame72 is preferably 50 milli-seconds (ms) with the interval 80 varyingaccording to the below listed equation.Interval length=standard length*(beta*standard length)

-   -   Where: interval length is the length of time in ms between data        frames;        -   Standard length is a predetermined duration of time in ms;            and        -   Beta is a random variable with a value between 0 and 1.

Preferably the standard length of time is 100 ms; therefore the intervallength will vary between 100 ms and 200 ms depending on the value ofbeta. Each transmission from the sensor assemblies 14 are sent withdiffering variable intervals 80, such that even if one or more datapackets 72 overlap for any one transmission, subsequent data packets 72will not overlap, thereby preventing cyclical, or repeated overlap. Asappreciated, differing intervals and lengths of data frames are withinthe contemplation of this invention, and a worker skilled in the artwould recognize the application of this method to other lengths of datatransmission.

In another embodiment of this invention, the length of the variableinterval 80 is transmitted to the receiver assembly 16. The receiverassembly 16 will then expect the next data packet 72 at the communicatedinterval. This allows the receiver assembly 16 to switch back to the ASKreceiver between data frames 72.

Another factor considered in preventing signal collision is thetransmission rate. The faster data is transmitted and received the lowerthe probability of data collision. Prior art FIG. 10 illustrates thelikelihood of signal collisions at a transmission rate of 4 kbaud. Eachline represents the length of time required to transmit each data frame72 from each of the sensor assemblies 14. FIG. 11 illustrates how theincrease in baud rate decreases the probability of overlapping dataframes 72. Each line represents a length of time to transmit one dataframe 72 to the receiver assembly 16. The shorter the total transmissiontime, the lower the probability of signal collision. Preferably, thesystem of this invention includes a baud rate of 10 kbaud as shown inFIG. 11, however, a worker skilled in the art would understand thatdifferent data transmission rates are within the contemplation of thisinvention.

Referring to FIGS. 1 and 12 the receiver assembly 16 comprises an ASKreceiver 52 and a FSK receiver 58. The FSK receiver 58 receives signalsfrom the sensor assemblies 14. The ASK receiver receives signals from akey fob 22 for the remote keyless entry system 19 to initiate theunlocking of doors 20. The receiver assembly 16 also includes an antenna48 to receive transmissions from the key fob 22 and the sensorassemblies 14. The receiver assembly 16 includes a low frequency driver50 to emit a signal to the sensor assemblies 14 to initiate transmissionby the sensor assemblies 14.

The antenna 48 is preferably of a length one quarter that of thewavelength of the transmission received. Transmissions received by theantenna 48 proceed through a resistor 54 to the RF receiver 16. Acontroller 60 controls which of the receivers 58 and 52 are engaged toreceive incoming transmissions.

Transmission from the various sensor assemblies 14 include the uniqueidentity code 68 (FIG. 8) relating to a specific sensor assembly 14. Theinitialization or learning mode defines the specific sensor assemblies14 disposed on a specific motor vehicle. Learning the specific identitycodes 68 of each of the sensor assemblies 14 eliminates errant receptionof other transmissions from other sensor assemblies 14 installed onother motor vehicles. Initialization occurs by matching the sensorassemblies 14 of a specific motor vehicle with the receiver assembly 16of that motor vehicle. The receiver assembly 16 disposed within themotor vehicle 10 will receive numerous signals from surrounding RFtransmitting sources such as radios, electrical appliances and othervehicle systems equipped with similar tire sensing systems.

Referring to FIG. 13, an embodiment of initialization includes placingthe receiver assembly 16 (FIG. 1) in a learn mode and actuating eachsensor assembly 14 through the use of a triggering device, schematicallyshown at 84. The triggering device can be a magnet, a transponderlocated at a programming station or a low frequency emitter positionedon the motor vehicle. The triggering device 84 initiates each sensorassembly 14 in sequence to transmit the identity code 68. The sequenceof initiating transmission of the identity code 68 indicates thelocation of the sensor assembly 14 on the motor vehicle 10. The firstsensor assembly 14 triggered is the front left tire, the second is thefront right and so on until all the tires on the motor vehicle have beentriggered to transmit the identity code 68 to the receiver assembly 16.The identity code 68 is stored sequentially to indicate the position ofthe specific sensor assembly 14. The receiver assembly 16 learns whichsensor assembly 14 belongs to the specific motor vehicle. In addition tothe specific location on the sensor assembly on the motor vehicle suchas the front right or front left tire is also recorded in the receiverassembly 16. This operation is repeated any time the tires 12 of themotor vehicle are changed or rotated.

Another embodiment of initialization requires no external trigger.Instead an acceleration value from the motor vehicle 10 is communicatedto the vehicle controller 18 and compared to accelerometer datatransmitted from each of the sensor assemblies 14. The accelerometer 34of each sensor assembly 14 transmits acceleration information of thetire 12. The acceleration value of each tire 12 is compared to theacceleration value provided by another vehicle system, such as theanti-lock braking system or transmission system (indicated schematicallyin FIG. 1 at 86). If the acceleration signals are equal within apredetermined tolerance value, the identity code 68 sent within thetransmission from the sensor assembly 14 will be recorded as belongingto the specific motor vehicle.

The initialization or learning process using the compared values ofacceleration may be repeated whenever the motor vehicle 10 is in anon-moving position for a predetermined length of time. The purpose ofthe re-learning of the sensor assembly identification codes is to allowfor changing or rotating of the tires 12 and thereby the sensor assembly14. The predetermined amount of time allows for the possibility that oneof the sensor assemblies 14 may have been changed, for instance when aspare tire is installed.

In the instance, where a new tire, and thereby a new sensor assembly 14is installed, the receiver assembly 16 receives the new identity code ofthe new sensor assembly 14 during initial movement of the motor vehicle10. The receiver assembly 16 compares the acceleration signal belongingto the new identity code of the new sensor 14 and compares it to theacceleration of the vehicle 10. If the vehicle acceleration iscomparable, the receiver assembly 16 will recognize the new sensorassembly 14 after a predetermined amount of time or number of dataframes. This is transparent to the operator of the motor vehicle.

Referring to FIG. 14, in another embodiment of this invention,localization of each of the sensor assemblies 14 is established bycomparing data obtained from another vehicle system 86 indicative of aturn of the motor vehicle 10. The tires 12 of a motor vehicle traveldifferent distances when turning. The inner tires 88 travel along afirst radius indicated at r1 and the outer tires 90 move along a secondradius r2. Acceleration and turning data is compared to the accelerationat each wheel. Data transmitted from a sensor assembly 14 mounted to oneof the inner tires 88 of the motor vehicle will indicate a loweracceleration than that of a sensor assembly 14 mounted to on of theoutside tires 90. Therefore, the side that the sensor assembly 14 ispositioned is indicated by the magnitude of acceleration of that tirerelative to the acceleration and direction of the motor vehicle 10.Accelerometer correlation determines whether the sensor assembly is onthe left or right side of the motor vehicle 10, however, this does notindicate whether the sensor assembly 14 is a front or rear tire.

In one embodiment of localization the front to rear location of the tire12 is accomplished by detecting signal strength of the transmission sentfrom each of the sensor assemblies 14. In this embodiment, the receiverassembly 16 includes front and rear antennas 92, 94. Transmissionsreceived at each antenna 92,94 are measured for field strength. The rearantenna 94 will receive transmissions having higher field strength fromthe sensor assemblies 14 disposed on the rear tires of the motor vehicle10. The front antenna 92 will receive a stronger transmission fromsensor assemblies 14 disposed on the front tires of the motor vehicle10. The field strength data provides the data indicating the front orrear position of each sensor assembly 14 and the acceleration datacorrelated to the turning radius of the motor vehicle 10 provides theleft or right position of each of the sensor assemblies 14.

Referring to FIG. 15, another embodiment of localization combines lowfrequency transmissions with correlation of acceleration to determinethe position of the sensor assemblies 14. Low frequency emitters 96 arepositioned to initiate transmission from the rear sensor assemblies 14.A transmission from the low frequency emitter triggers the transmissionof the rear sensor assemblies 14 that is then received by the receiverassembly 16 to indicate a rear location of the tires 12. This providesthe data required to determine the front and rear position of anyparticular sensor assembly 14. The left and right position is determinedby correlating accelerometer data obtained from each of the sensorassemblies 14. Further, a worker knowledgeable in the art will recognizethat other combination of low frequency initiating transmissions andcorrelation of accelerometer data can be used to determine the specificlocation of any of the sensor assemblies 14 disposed on the motorvehicle 10.

The receiver assembly 16 of this system is also used with the remotekeyless entry system 19. The receiver assembly 16 is configured toreceive transmission from both the sensor assemblies 14 and the key fob22 (FIG. 1). Although a key fob 22 is specifically described it iswithin the contemplation of this invention that the remote entry system19 include other active or passive transmitting means to initiate entryor operation of the motor vehicle 10.

The receiver assembly 16 includes the ASK receiver 52 and the FSKreceiver 58. This configuration allows the receiver assembly 16 to beused for both the remote keyless entry system 19 and the tire monitoringsystem.

ASK transmissions are favorable for situations where the transmitter andreceiver are substantially stationary. The ASK radio frequencytransmission is easily disrupted by abrupt changes in received fieldstrength and therefore are not favorable sending transmission from amoving object such as the tires 12 of a motor vehicle 10. The changesfrom received field strength can change for any number or reasons withina motor vehicle including interference created by other onboard systems,to the specific environment present at the time of the signal. However,the ASK provides for greater signal power which is desirable for theremote keyless entry system of this invention. The ASK transmissionallows for higher peak output field strength, relative to a comparableFSK transmission. However, the ASK transmission decreases typicalbattery life and is therefore not desirable for applications such astire condition sensing that require longer battery life due to thedifficulty of changing batteries of the sensor assemblies disposedwithin the tire of the motor vehicle.

FSK transmissions are favorable for conditions were the transmitter orreceiver is moving during data transmission. As appreciated, rotation ofa tire will introduce amplitude variations in the transmission caused bythe changes in interference patterns. If sensor assembly 14 data wastransmitted by way of an ASK transmission, the noise caused by rotationof the tire would cause data in the transmission to become corrupted.However, an FSK transmission is amplified upon receipt to effectivelyremove any amplitude disturbances. Further, the FSK transmission is lesspower intensive and therefore more adaptable to the sensor assemblyapplication that requires longer battery life.

Referring to FIG. 12, the receiver assembly 16 defaults to sending anytransmission to the ASK receiver 52. The ASK receiver 52 operates at alower power and is therefore the default receiver that is on when thereceiver assembly 16 is activated. The ASK receiver 52 is engaged whilethe motor vehicle 10 is stopped or parked. Preferably, the ASK receiver52 is engaged in response to the speed of the motor vehicle being belowa predetermined speed. Preferably, the predetermined speed is 10 mph.Above 10 mph, the receiver assembly 16 will change over to the FSKreceiver 58. The switch is initiated because it is unlikely that theremote keyless entry system 19 will be activated while the vehicle 10 istraveling at speed. The FSK receiver 58 will then receive transmissionsfrom the sensor assemblies 14.

The conditions of the motor vehicle 10 traveling above the desired speedor in a parked position provide definite indicators for the switchbetween FSK and ASK receivers 58, 52. However, when the vehicle 10 isidling, for instance in a traffic jam, but not moving at the desiredspeed to switch from the ASK receiver 52 and the FSK receiver 58 thesystem will not switch over to the FSK receiver 58 unless anotherconditions is satisfied. Each transmission 64 (FIG. 8) includes the ASKwake up signal 66 that is sent prior to the FSK transmission. The ASKwake up signal 66 alerts the receiver assembly 16 to incoming FSKtransmission, which causes the receiver assembly 16 to switch over tothe FSK receiver 58. The switch over allows the receiver assembly 16 toaccept data indicative of tire conditions from the sensor assemblies 14while the automobile is parked or idling in traffic.

Preferably, each of the sensor assemblies 14 will transmit a signalindicative of tire conditions at differing rates depending on the speedof the motor vehicle. At speeds above a predetermined speed the sensorassemblies 14 will transmit tire condition data at a greater frequency.At lower speeds, indicative of a parked vehicle, the sensor assemblies14 transmit at a lower rate. Preferably, the predetermined speed is 10mph and the sensor assemblies 14 will transmit signals indicative oftire conditions once every minute. Below the 10 mph predetermined speedthreshold the sensor assemblies 14 will transmit signals only aftersensing a change in tire pressure above a desired amount indicative of atire 12 losing air pressure. Once an initial loss of pressure is sensed,the sensor assemblies 14 are triggered to transmit signals at one-minuteintervals. Although, specific speeds and intervals of data transmissionare discussed, a worker knowledgeable in the art will understand that itis within the contemplation of this invention to use other speeds anddata transmission intervals according to specific application criteria.The selective actuation of the transmitter 40 for each sensor assemblyand the switching between the ASK and FSK receivers 52,58 prevent signalcollisions between ASK and FSK transmission emitted by the remotekeyless entry system 19 and the tire monitoring system. Preventingsignal collisions optimizes function of the receiver assembly 16.

The foregoing description is exemplary and not just a materialspecification. The invention has been described in an illustrativemanner, and should be understood that the terminology used is intendedto be in the nature of words of description rather than of limitation.Many modifications and variations of the present invention are possiblein light of the above teachings. The preferred embodiments of thisinvention have been disclosed, however, one of ordinary skill in the artwould recognize that certain modifications are within the scope of thisinvention. It is understood that within the scope of the appendedclaims, the invention may be practiced otherwise than as specificallydescribed. For that reason the following claims should be studied todetermine the true scope and content of this invention.

1. A system for monitoring conditions within a tire comprising: a sensorassembly disposed within each tire of a motor vehicle, a transmitter incommunication with said sensor assembly to transmit a frequency shiftkeyed transmission indicative of current tire conditions; a remotetransmitter for actuating a remote keyless entry system, said remotetransmitter emitting an amplitude shift keyed transmission to actuate afunction of said keyless entry system; a receiver assembly for receivingsaid frequency shift keyed transmission signal indicative of saidcurrent tire conditions and said amplitude shift keyed transmissionsignal to actuate a function from said remote transmitter, wherein saidtransmission indicative of current tire conditions includes an amplitudeshift keyed wake-up signal for alerting said receiver assembly of anincoming frequency shift keyed transmission signal.
 2. The system ofclaim 1, wherein said receiver assembly includes an amplitude shiftkeyed receiver, and a frequency shift keyed receiver, said amplitudeshift keyed receiver and said frequency shift keyed receiver areselectively engaged to receive incoming signals in response to apredetermined triggering event.
 3. The system or claim 2, wherein saidpredetermined triggering event is the current speed of the motorvehicle.
 4. The system of claim 3, wherein said amplitude shift keyedreceiver is engaged to receive incoming signals for speeds below apredetermined speed threshold of the motor vehicle and said frequencyshift keyed receiver is engaged to receive incoming signals for speedsabove said predetermined speed threshold.
 5. The system of claim 2,wherein said amplitude shift keyed wake up single initiates a switchfrom said amplitude shift keyed receiver to said frequency shift keyedreceiver.
 6. The system of claim 1, wherein said transmitter sends saidsignal at predetermined intervals, said predetermined intervals variedin response to motor vehicle speed.
 7. The system of claim 1, whereinsaid predetermined interval is greater at speeds above saidpredetermined speed threshold than below said predetermined speedthreshold.
 8. The system of claim 7, wherein said predetermined intervalincreases in response to variation of pressure within one of said tires.9. The system of claim 1, wherein said transmission indicative of saidtire conditions includes a plurality of data frames sent at random timeintervals to prevent repeated overlap of transmissions from two or moreof said sensor assemblies.
 10. The system of claim 9, wherein saidrandom time interval is transmitted to said receiver assembly such thatsaid receiver assembly anticipates subsequent data frames of saidtransmission indicative of said tire condition.
 11. The system of claim10, wherein said amplitude shift keyed receiver is engaged during saidrandom time interval.
 12. The system of claim 1, wherein said receiverassembly includes a learning mode for discerning between signals fromsensor assemblies disposed on other motor vehicles; said learning modecompares an acceleration value obtained from said sensor assembly with avehicle acceleration value to distinguish between sensor assembliesdisposed on another motor vehicle.